April's presidential poll will be the first time in almost 20 years that elections have been held by a civilian government.

According to the BBC's Sola Odunfa in Lagos, Mr Obasanjo - a Christian from the south-west - has alienated much of the support in the largely Muslim north that helped him to victory four years ago, and Muslim power brokers have made it very clear that they are now looking to alternative candidates.

The PDP vote had been expected to be a close contest, but reports suggest a private meeting held on Saturday led the PDP's state governors to throw their support behind Mr Obasanjo.

Mr Obasanjo's election victory in 1999 sealed the end of the most recent period of military rule in Nigeria.

His challenge now will be to win the support of voters from the country's Muslim north, where many see him as a southern Christian president who has failed to meet their aspirations.